1. Field of the Invention
The present invention relates to a method of producing an ion sensitive working electrode for a heavy metal ion sensor. The electrode includes a mixture of Ag.sub.2 S and Mes, with Me being the heavy metal to be determined.
2. Background of the Related Art
Together with a measuring solution containing the heavy metal ions to be determined and with a reference electrode, preferably an Ag/AgCl reference electrode, the mentioned working electrode constitutes a heavy metal ion sensor. The principle of such sensors is described, for example, in the book by Cammann, entitled "Das Arbeiten mit ionensensitiven Elektroden" [Working With Ion Sensitive Electrodes], published by Springer-Verlag, Berlin, Heidelberg, New York, 1977, particularly pages 59-66. Such conventional working electrodes are relatively large. They also break easily because a glass tube is employed as the casing. A particular drawback is that they are relatively expensive to manufacture (approximately DM 200.00 to 800.00 retail price each). Moreover, only a single heavy metal can be detected with the prior art sensor.
DE-OS 3,639,312 corresponding to U.S. Pat. No. 4,908,118 discloses a solid state electrode for the determination of sodium concentrations in solutions; this electrode is produced in thick-film technology. The various layers are here applied on top of one another and next to one another onto a substrate to form together the solid state electrode. If necessary, the layers are provided with a cover which exposes and permits access to the solid state electrolyte membrane provided there. However, with this prior art solid state electrode it is not possible to detect heavy metal ions. And again only a single material can be detected, namely the concentration of sodium ions in solutions.
Similar prior art is disclosed in DE-OS 3,639,802 which discloses a sensor produced in thick film technology for monitoring the hydrogen concentrations in gases.
Additionally, reference is also made to British Patent 2,102,963-A which discloses several embodiments of an ion selective electrode in the form of a film, with the electrode including a conductive layer and an ion selective layer laminated thereon so as to cover at least one edge of the conductive layer.
Based on a method including the above-mentioned features, it is therefore an object of the present invention, to develop this method in such a way that an economical manufacture results in a working electrode whose sensor is able to detect different heavy metals. The sensor should be easily miniaturized and easily manipulated; in particular, it should not be fragile.